The present invention relates to a contour emphasizing circuit, wherein a digital contour-emphasized video signal on the basis of the input of an analog signal is output, and is employed to provide contour-emphasized color video signals for a display device (for example, matrix type display device) which is digitally driven such as a plasma display (referred only to as PDP) and liquid crystal display (referred only to as LCD).
In the conventional CRT (Cathode Ray Tube) display device, the contour emphasizing processing is being carried out aiming at the high picture quality implementation and high pass characteristic compensation. The contour emphasizing circuit to carry out this contour emphasizing processing is, as shown in FIG. 1, composed of a Y/C separation circuit 10, a color demodulation circuit 12, a contour extracting circuit, phase adjustment circuits 16, 18 and 20, an adder 22 and a matrix circuit 24.
The Y/C separation circuit 10 separates a Y (luminance) signal and a C (color) signal from the composite video signal (for example, compound color television signal) input to an input terminal 26, and the color modulation circuit 12 separates a Y signal, an Rxe2x88x92Y (color difference) signal and a Bxe2x88x92Y (color difference) signal on the basis of a Y signal and a C signal.
The contour extracting circuit 14 extracts the contour component Ye which is a high-pass component of a video signal on the basis of an adder 22.
The matrix circuit 24 prepares a signal adding the contour component Ye to the R (red), G (green) and B (blue) signals, respectively, on the basis of (Y+Ye) signals added by the adder 22, an (Rxe2x88x92Y) and a (Bxe2x88x92Y) signal phase-adjusted by phase adjustment circuits 18 and 20. That is to say, the matrix circuit 24 prepares R+Ye, G+Ye and B+Ye on the basis of the operations in following equations (1), (2) and (3). By outputting these R+Ye, G+Ye and B+Ye to the CRT display device by means of output terminals 28r, 28g and 28b, videos contour-emphasized by this CRT display device are displayed.
(Rxe2x88x92Y)+(Y+Ye)=R+Yexe2x80x83xe2x80x83(1)
(Gxe2x88x92Y)+(Y+Ye)=G+Yexe2x80x83xe2x80x83(2)
(Bxe2x88x92Y)+(Y+Ye)=B+Yexe2x80x83xe2x80x83(3)
(Gxe2x88x92Y) in the above equation (2) is generated by the following equation (4).
In case of a video contour-emphasized by a matrix type display device driven by digital video signals (for example, R, G and B signals) like PDP and LCD is displayed, each signal of (R+Ye), (G+Ye) and (B+Ye) obtained in output terminals 28r, 28g and 28b in FIG. 1 is output to the display device after being digitized by the A/D (analog/digital) conversion circuit. However, in such a prior example, in case a large amplitude signal is input to an input terminal 26, or in case the contour emphasizing quantity (or contour emphasizing coefficient, the description is omitted, as it is similar afterwards) is xe2x80x9clargexe2x80x9d, there is a problem that the correct operation cannot be obtained over the dynamic range of A/D conversion circuit.
For example, in case a large amplitude signal is input in the input terminal 26, by outputting a signal over the dynamic range of an A/D conversion circuit as shown at the left-hand side in FIG. 2(a) from output terminals 28r, 28g and 28b, there are problems that signals exceeding an upper conversion reference voltage value VRT (for example, 5 volts) in the dynamic range as shown at the right-hand in said figure (a) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRT (for example, 3 volts) in the dynamic range are cut, resulting in producing black crushing.
Further, in case the contour emphasizing quantity of the contour extracting circuit 14 is xe2x80x9clargexe2x80x9d, there are problems that signals over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG. 2(b) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRB are cut, resulting in producing black crushing.
The present invention is carried out taking into account said problems, and even when a large amplitude signal, wherein white crushing or black crushing is input in the contour emphasizing circuit in FIG. 1, or even when the contour emphasizing quantity is xe2x80x9clargexe2x80x9d, aims at providing a contour emphasizing circuit that can display a contour emphasizing video without white crushing or black crushing in a display device driven by a digital video signal.
The contour emphasizing circuit according to the present invention is characterized by being provided with an A/D conversion circuit to convert analog color video signals (for example, R, G and B signals) to digital color video signals, a Y signal generation circuit to generate a Y signal from these digital color video signals, a contour extracting circuit to extract a contour component from the generated Y signal, and a contour adder to output a signal contour-emphasized by adding the extracted contour component to the digital color video signals output from the A/D conversion circuit.
Since a Y signal is generated after analog color video signals are converted to a digital signal by the A/D conversion circuit, and the contour component extracted from this Y signal is added to digital color video signals output from the A/D conversion circuit, there is no contour emphasizing component over the dynamic range of A/D conversion circuit as with the prior example. For this reason, in case analog color video signals to input in the contour emphasizing circuit of the present invention are large amplitude signals, or even in case the contour emphasizing quantity is xe2x80x9clargexe2x80x9d, in case a signal output from the contour emphasizing circuit of the present invention is output to the display device driven by a digital video signal and a contour emphasizing video is displayed, neither white crushing nor black crushing is produced.
Hence, to output a video signal adding a vertical contour component and a horizontal contour component and to be able to display a video emphasizing contours in vertical and horizontal directions, the contour extracting circuit comprises first and second line memories, a vertical contour extracting circuit, a contour emphasizing frequency setting circuit, a horizontal contour extracting circuit and a contour synthesis circuit.
Further, to simplify the circuit configuration of the contour emphasizing frequency setting circuit, it comprises 1-dot delay elements of four contour emphasizing frequency setting circuits connected in series, a Y signal of 2-dot delay is output from the second 1-dot delay element, and a Y signal of 4-dot delay is output from the fourth 1-dot delay element.
Further, to avoid a noise influence, in the contour extracting circuit, a core ring circuit to suppress the contour component of less than a level is provided.
Further, to make the contour emphasizing quantity large, a gain controller to adjust the size of the contour component extracted in the contour extracting circuit and a coefficient multiplication circuit to output to the contour adder after multiplying by coefficients Kr, Kg and Kb.